The invention relates to a blocking device for a safety belt having a belt retractor, which comprises a belt reel for winding and unwinding the safety belt, a toothed control wheel rotating with the belt reel and controlled in a safety-belt sensitive and/or vehicle-sensitive manner, and a control plate, which is coupled in the event of triggering to the control wheel and is disposed so as to be pivotable between a disengaged position and a blocking position. The pivoting movement into the blocking position is effected by a pull on the safety belt in the belt withdrawal direction and leads via a blocking mechanism to blocking of the blocking device, whereby a vehicle sensor effects engagement of a sensor pawl into an associated toothing of the control wheel and/or a safety belt sensor controls a sensor pawl which couples the control wheel and the control plate to one another through engagement into an associated toothing.
A blocking device of the aforementioned kind is known in various embodiments, e.g., from European Patent Application 0 185 367 or European Patent 0 307 822. In these embodiments, the belt retractor of the blocking device is combined with a clamping device as a blocking mechanism for the safety belt, the movable clamping jaw of the clamping device being connected to the pivotable control plate of the belt retractor in such a way that the pivoting of the control plate, effected by the control system of the belt retractor with the control wheel, is converted into the clamping motion of the clamping device. In this embodiment it is immaterial whether the control wheel or the associated control mechanism of the belt retractor is disposed on the control plate itself so that, with the pivoting of the control plate, the belt reel is also radially displaced, or whether the belt reel together with the control wheel is supported in a radially fixed manner and the separately disposed control plate may swivel about the axis of the belt reel or the control wheel. A blocking device of the aforementioned kind, in which the blocking mechanism is formed by a self-locking belt retractor having a belt reel which is radially displaceable into a blocking toothing fixed to the housing, is moreover disclosed in European Patent Application 0 112 033.
With a belt retractor as part of a blocking device constructed as described above as part of a blocking device, a rapid intake of the safety belt at the end of a belt winding process may lead to self-blocking of the control mechanism in that, upon a resultant activation of the safety belt sensor or the vehicle sensor, the respective sensor pawl moves into engagement with the associated toothing of the control wheel and in so doing effects the coupling to the control plate so that, at the end of the winding process, the belt retractor is in a state of readiness for blocking, in which any pull on the safety belt in the belt withdrawal direction necessarily leads to a blocking of the blocking device either because the consequently triggered swivelling of the control plate operates the clamping jaw as a blocking mechanism or because the belt reel is displaced radially into its locking position. Because the toothings on the control wheel are usually constructed with a specific undercut or because of friction between sensor pawl and gearing, the readiness for blocking is no longer automatically releasable when the safety belt is fully taken up because there is no longer any length of safety belt which may be drawn in to effect a rotation of the control wheel which frees the associated sensor pawls and releases the self-blocking action. This self-blocking action is a particular drawback in the case of belt retractors connected to a clamping device because a withdrawal of the safety belt is prevented by the clamping device activated upon each pull on the safety belt. In general, by applying a certain pull on the safety belt, it is still possible in conventional belt retractor, based on the film reel effect, to bring about a releasing rotation of the control wheel; however, with a clamping device connected on the load side, this is not possible. The same applies, however, also to self-locking belt retractors which are combined with automatically operating adjusting systems because, when belt withdrawal is inhibited by self-blocking of the belt retractor, an activation of the adjusting system may lead to the destruction of structural parts.
The object of the present invention is thus to improve a blocking device of the aforementioned kind in such a way that a self-blocking action of the associated belt retractor may be canceled by a single pull on the safety belt.